Equipment rotational molding

A number of factors should be taken into account in the design of a rotomolding process, regardless of the type of the rotational molding equipment. A list of the items to be considered is provided in Table 9.3. 

The term dispersion refers to how well the pigments are wetted out in the plastic matrix (see below), whereas distribution refers to the uniformity of color in the part. Finally, in referring to the parts fabrication process, the term molder is used below to represent any the following pieces of equipment injection molding machine, injection or extrusion blow molding machine, or rotational molding machine. 

With the exception of two fluoropolymers, PVF and PTFE, the rest of the resins described in this entry can be processed by standard melt-processing techniques, such as injection, transfer and blow molding, extrusion, and rotational molding. Process equipment for fluoropolymers must be made from corrosion resistant alloys because of the corrosive compound that may be produced when fluoropolymers are heated above their melting points. Higher melt viscosity of these resins may require more powder and higher pressure rating equipment. 

Figure 8.8 Schematic of rotolining equipment showing the four principal stages of rotational molding. (Courtesy RMB Products, Fountain, CO.)...

Playground Equipment market (Figure 14.21). In Europe the leading markets are Food and Agriculture (27%) and Industrial Applications (7%). In Mexico, where rotational molding is very popular, water tanks represent 90% of all goods produced. 

Rotational molding utilizes a closed female mold. The mold is opened and filled with a predetermined weight of powder or liquid. It is then swung into the oven section of the equipment and rotated around its primary and secondaiy axes. The oven heats the mold which, in turn, heats the powder. As the powder melts, it deposits imiformly on the interior walls of the mold. When all the material is deposited on... 

Typical applications of rotational molding include chemical tanks, automotive and commercial aircraft parts, backyard play equipment, toys, etc. Rotational molding requires long cycle time, which puzzles the overall success of the technology. The cycle times are restricted by the time required to heat up and cool down the mold and the product by the slow heat convection process. 

Rotational Molding and Blow Molding. Rotational molding accounts for approximately 5% of LLDPE consumption and blow molding accounts for approximately 0.5%. Rotational-molded articles include storage tanks, shipping containers, recreational equipment, and outdoor furniture. LLDPE has higher impact... 

Equipment. The eqnipment used in rotational molding is simple many variations are available. The most common type is the so-called carousel type (Fig. 1). This machine consists of a heating station or oven, a cooling station (frequently an enclosed chamber), and a loading and imloading station. A carousel has three to six spindles or arms where the mold or molds are moimted. Most carousels have the freedom to revolve in a complete circle. The spindles are moimted on a central hub and driven by variable motor drives. New control systems allow each arm to operate independently in movement and control of oven temperature and time. Microprocessors are incorporated in the control system. Computer simulation software can be utilized in prototyping and manufacturing. 

Compared with blow molding, rotational molding offers lower equipment and mold costs and broad design parameters. Blow molding, however, provides a quicker... 

Rotational molding is a reasonably safe industry. Most resins used are nonhaz-ardous. Some resins may cause mild irritation suppliers provide safety information on their handling and use. Most resins used for rotational molding are ground to 500 /xm (35 mesh), and appropriate procedures should be followed to prevent a dust explosion and fire. A rotomolder is a relatively safe piece of processing equipment fans are enclosed with guards spindles and arms operate at a low speed. The oven is equipped with a temperature control. 

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